A cross-flow fan, a fan assembly, and an air conditioner, wherein the cross-flow fan (1) comprises two end surfaces (12, 13), and a recess (14) is provided on one of the end surfaces. The cross-flow fan, the fan assembly, and the air conditioner can prevent water from entering a bearing fixing base via the end surfaces of the fan and corroding a bearing rubber ring, and can prevent excessive noise from generating and affecting user experience when the air conditioner is in operation.